Circuit module having force resistant construction

ABSTRACT

Impact resistant circuit modules are disclosed for enclosing a die having a sensor area. Preferred modules include a flexible circuit and a die coupled thereto. The flexible circuit is preferably folded over compressible material to help absorb applied forces. A gap may be provided between sides of the die and the compressible material to help prevent peeling. A metal reinforcing layer may be bonded to the back of the die. A low modulus material including a patterned gap underneath the die may be used to absorb forces. A dry film adhesive may be placed between at least part of the upper surface of the die and the flexible circuit, preferably to provide further point impact resistance and protection. High and low modulus material may be combined in ruggedizing structures. Consumer devices employing such circuit modules are also taught, as well as module construction methods.

FIELD

The present disclosure relates to enclosures or packaging forsemiconductor dies, and especially to packaging sensors for relief ofstresses associated with their use.

BACKGROUND

Many sensors, including fingerprint sensors, exist as part of asemiconductor die having micro-component transducers such as antennas.One popular fingerprint sensor is presented on a semiconductor die as anarray of radio frequency (RF) antennas that receive low powertransmissions directed to reflect from a user's finger presented abovethe array. One typical application of such a sensor, for example, is alaptop computer provided with a fingerprint sensor pad at one externalsurface. The laptop or other device may employ, mounted near an outersurface, a fingerprint scanner (or other biometric device), such as the“FingerLoc® 8600” (AFS8600) manufactured by AuthenTec. In such a case,the die may have a sensing area that comprises an RF fingerprint sensingarray, which may be externally exposed as a sensor pad. The user pressesa designated finger or thumb downward on the pad to identify themselvesto the device and gain access.

Pressing a finger on a sensor pad often causes mechanical force to beapplied to the sensor. In some cases, such force may overstress thestructure of the sensor and package by, for example, bending the die orbending the package sufficiently to crack or break conductive layerswithin the package, causing electrical failure. Because the sensor padis presented at an exposed surface, it may be subjected to other forcessuch as being struck or squeezed by common scenarios like the devicebeing hand-carried, dropped, or having object stacked on top of it.

Some previous sensor packages provide compressible material beneath thesensor array to help absorb such forces. However, such schemes typicallysuffer from a variety of problems. One problem is that a semiconductordie containing the sensor or sensor array may be bent by the stress andmay fail or crack as a result. Another problem is that downward forcesmay cause the sensor die to peel away from the flexible circuit to whichit is mounted. Still further, the forces applied to the sensor array maycause mechanical stress and failure at other parts of the sensorpackage, such as conductive traces, or output connection contacts, forexample.

What is needed are semiconductor circuit modules or packages that enablesemiconductor die or other sensor transducers to be presented along anouter surface of the package while still absorbing forces applied to thesensor sufficiently to prevent failure.

SUMMARY

This specification describes technologies relating to enclosures orpackaging for semiconductor dies, and especially to packaging sensorsfor relief of stresses associated with their use. In general, one aspectof the subject matter herein is a circuit module including a flexiblecircuit and a die electrically coupled to the flexible circuit. The diehas a sensing area. The flexible circuit is preferably folded over aninterior area, which is provided with compressible material to helpabsorb applied forces. In some preferred embodiment, a gap may beprovided between at least one side of the die and the compressiblematerial to help prevent the die peeling away from the flexible circuit,In some embodiments, the die may have a reinforcing layer or a highmodulus material attached to the bottom surface or disposed about thebottom surface and sides of the die in a manner sufficient to at leastpartially protect the die from flexural loads. Preferably, thereinforcing layer has a coefficient of thermal expansion closelymatching that of the die. Low modulus material may also be disposed inthe interior region and about the high modulus material in a mannersufficient to at least partially absorb compressive loads applied to thedie.

In some embodiments, the flexible circuit is preferably folded over aninterior area, which is provided with compressible material to helpabsorb applied forces. Low modulus material compressible material may beused including a patterned gap formed in the low modulus material underthe bottom surface of the die. Additionally, a dry film adhesive may beplaced between at least part of the upper surface of the die and theflexible circuit, preferably to provide further point impact resistanceand protection.

Consumer devices such as, for example, laptop computers, personaldigital assistants (PDAS), mobile phones, or other such devices, may beprovided with a circuit module 10. The module preferably is housed toplace the sensing area of the die along the outer surface or skin of theproduct, although some variants may have another covering, such as anaccess panel, above the sensor circuit module. Some devices have asecurity access system programmed to receive identifying data from asensor on the circuit module and provide device access based on theidentity or lack of an identifying match. Other devices may use thesensor data for other purposes.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,aspects, and advantages of the invention will become apparent from thedescription, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a circuit module according to one embodiment of thepresent invention.

FIG. 2 depicts an exemplar layout of a conductive layer of the flexiblecircuit according, to one embodiment of the present invention.

FIG. 3 depicts an alternate embodiment of the circuit module in whichthe die it contains is enclosed at least partially on five sides with areinforcing layer.

FIG. 4 depicts an alternate embodiment of the circuit module in which adry film adhesive bonds at least part of the upper surface of the die tothe flexible circuit.

FIG. 5 is an enlarged view of gap construction feature according toanother embodiment of the present invention.

FIG. 6 is a flow chart of a process for making a circuit moduleaccording to one embodiment of the present invention.

FIG. 7 is a flow chart of a construction process according to anotherembodiment of the present invention.

FIG. 8 is a flow chart of a construction process according to anotherembodiment of the present invention.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

FIG. 1 depicts a circuit module 10 according to one embodiment of thepresent invention. Circuit module 10 includes a flexible circuit 11 anda die 12 mounted on flexible circuit 11 so that it is exposed through apolyimide window along the top side 15 of flexible circuit 11. Forexample, die 12 may be a sensor chip with an exposed sensor array, wherethe array is exposed along the outside surface of anelectrically-connected operating environment of circuit module 10, suchas a consumer device. For instance, the circuit module 10 may employ diesuch as those used in the “FingerLoc® 8600” (AFS8600) manufactured byAuthenTec. In such a case, die 12 may be an exposed sensor module havinga sensing area that comprises an RF fingerprint sensing array. Such asensing area on die 12 could facilitate the process of counting ridgesin a fingerprint.

Flexible circuit 11 may be bent to form an interior region 13. Flexiblecircuit 11 contains one or more conductive layers connected to aconductive footprint 22 expressed along the bottom side 17 of flexiblecircuit 11 (the downward-facing surfaces of flexible circuit 11). Whenbent in such a way, flexible circuit 11 may form a portion of thesemiconductor package for die 12 while presenting the sensing area ofdie 12 to the outside of the housing. Sensor signals from die 12 arepreferably transmitted through a metal free window portion of theflexible circuit. Other sensor transducers may be used.

In one embodiment, the entire circuit module 10 may be mounted as a ballgrid array (BGA) device on the system board of a consumer device (e.g.,fingerprint scanner). In other embodiments, circuit module 10 may beleaded or another kind of package. In yet other embodiments, circuitmodule 10 may use any other suitable type of surface-mounted packaging,such as that used for integrated circuits.

In some embodiments, die 12 may be mounted above a reinforcing layer 14,such as a metal (e.g., an iron-nickel alloy) reinforcement. Such areinforcing layer 14 may be bonded to the back of die 12, serving toprotect die 12 from bending or damages from other forces when pressureis applied to the top side 15 of die 12. The construction material forreinforcing layer 14 may be chosen to have a high modulus of elasticity(e.g., of at least about 25 giga-Pascals), a high tensile strength(e.g., of at least about 70 mega-Pascals) necessary for constructing,and a coefficient of thermal expansion matching that of die 12sufficiently to prevent damage from different thermal expansion rates inthe desired application (e.g., within 5%, but preferably an exact matchor as close as possible, like within 1%). One preferred material is theInvar® nickel-iron alloy (FeNi36) which has a low coefficient of thermalexpansion (CTE) in the range from room temperature up to 230° C. Thisalloy is has machinability similar to stainless steel and typically doesnot suffer from stress corrosion cracking. Other suitable alloys ornon-metal reinforcing layers may be used, such as, for example, FeNi42.Such matching coefficients of thermal expansion can, for example,prevent thermal expansion stress faults in and between die 12 andreinforcing layer 14. Where a reinforcing layer is employed with gaps atthe side of the die, the gaps may extend parallel to sides of thereinforcing layer as well, may terminate above the reinforcing layer asdepicted, or terminate below the reinforcing layer.

Preferably, a portion or all of the sensing area of die 12 is protectedby a polyimide window 23 (FIG. 2), or one or more layers of some othersuitable high-performance protective film. For certain types of sensorarrays, such a layer is a metal-free zone to allow unobstructed sensingsuch as, for example, with reflected RF signals that pass through thepolyimide layer without deleterious reflection or excessive attenuation.

Die 12 (plus its stacked reinforcing layer 14) may be mounted above aresilient low modulus material 16 to absorb loads applied to die 12. Forexample, having resilient low modulus material 16 with a lower elasticmodulus than that of die 12 may help prevent damage to the die surfacefrom excessive force applied to a small area of the die's surface.

In some embodiments, a gap pattern 18 may exist between the bottom ofthe reinforced die 12 and the resilient low modulus material 16. Gappattern 18 may consist of voids shaped to provide bumps between thevoids, or gap pattern 18 may consist of multiple ridges having voids inbetween, The gap pattern (or “patterned gap”) may be formed of voidsshaped to provide, between the voids, bumps that soften initialresistance of the low modulus material to downward compressive forces onthe die. The bumps or the ridges (or other suitable shapes) may softeninitial resistance of the low modulus material 16 to downwardcompressive forces on die 12, such as to provide an initial pressurerelief when a force is applied to the exposed outer surface of die 12.While angular bums are shown, other bumps such as smoothly curved bumpsor half-circles may be used. Gap pattern 18 may cover the entire bottomof the reinforced die 12, or the surface of the resilient low modulusmaterial 16 may be patterned (with bumps, for example) so that initialdisplacement sees a soft force, and the force increases with additionaldisplacement. Outside pressure initially compresses the flex against thesurrounding resilient pad. The reinforced die 12 may be restrained fromdisplacement only by the flexible circuit, the polyimide window thereof,and/or contact with any gap pattern 18 in the supporting the resilientlow modulus material 16. Additional displacement may result in verticalsupport being supplied by contact with the bulk of the resilient lowmodulus material 16 below gap pattern 18.

The area around die 12 on the top side 15 of flexible circuit 11 may besubstantially larger than the die area itself. In some embodiments, die12 may be surrounded by gaps 20 between the edges of die 12 and theproximate edges of the resilient low modulus material 16. Such gaps 20may reduce “peel force” when downward force is applied on the topsurface of die 12. For example, gaps 20 may reduce the concentration ofstresses along the edges of die 12 when forces on the top surface of die12 would otherwise have the tendency to peel the flex away from the die.

The module 10 is depicted mounted to circuit board in operatingenvironment 5 which is preferably consumer device or security devicesuch as, for example, a laptop computer, personal digital assistant,mobile phone, access panel, or other such device. Other module mountingschemes may be employed, such as flexible circuit or circuits in which amodule 10 is part of a larger circuit module, for example. The modulepreferably is housed to place the sensing area of the die along theouter surface or skin of the product, although some variants may haveanother covering, such as an access panel, above the sensor circuitmodule. Some devices have a security access system programmed to receiveidentifying data from a sensor on the circuit module and provide deviceaccess based on the identity or lack of an identifying match. Otherdevices may use the sensor data for other purposes.

FIG. 2 depicts an exemplar layout of a conductive layer 52 of flexiblecircuit 11 according to one embodiment of the present invention. Theexemplar layout of conductive layer 52 depicted in FIG. 2 is shown fromthe side to which die 12 will be mounted. The layer is shown flat, butflexible circuit 11 may be bent when circuit module 10 is assembled.Specifically, flexible circuit 11 may be bent such that die 12 ispresented underneath window portion 23 of the flexible circuit, with itssensor area oriented toward top side 15 of flexible circuit 11externally exposed through a polyimide layer.

Referring to FIG. 2, in this embodiment conductive layer 52 has an arrayof gold contacts 27, which are preferably gold pads, arranged as fourrows in a square for attaching with thermal compression to oppositelydisposed contacts formed on die 12. Other embodiments may have adifferent arrangement of contacts 27, such as, for example, pads orbumps of copper, aluminum, or other suitable conductive metals. Goldpads are preferred, with corresponding gold bumps oppositely formed onthe die for attachment. Those of skill will recognize that the one ormore rows of contacts 27 may be referred to as an “array” or “footprint”for connecting a component, a flip-chip, or a bare die such as usedherein. There may be other footprints expressed by conductive layer 52for connecting additional components, such as additional arrangements ofcontacts 27 around each of multiple dies 12.

Depicted are exemplar traces 42 (e.g., made of copper) at the level ofconductive layer 52. Traces 42 connect contacts 27 to flex contacts 54.The flexible circuit may have multiple conductive layers 52 with crosstraces such as the depicted dotted-line trace 42 in FIG. 2. Flexiblecircuit construction is known in the art, and a variety of techniquesmay be employed to design the flex circuits described herein. Forexample, flexible circuit techniques are taught in U.S. patentapplication Ser. No. 10/435,192 by Roper, et al, which application isowned by the present assignee and is hereby incorporated by reference inits entirety for all purposes. Some embodiments may have a singleconductive layer flex circuit. In some embodiments, flex contacts 54 mayconductive pads for attaching a ball grid array 19 or some other type ofsurface-mount packaging interconnect used in integrated circuits, suchas low profile contacts constructed with pads and/or rings that areconnected with solder paste applications to appropriate connections. Theflex contacts 54 shown here may be electrically connected to conductivefootprint 27 of FIG. 1.

Inside of footprint 27 is depicted a polyimide “window” or metal freezone 23. Die 12 is preferably mounted to position its sensing arrayfacing window 23 for optimum direction of sensors to acquire datathrough window 23. The die sensing area exposed, either underneathpolyimide window 23 or protected in some other suitable manner, may bereferred to as a sensor pad or sensor panel, depending, of course, onthe number and type of sensors provided on the die sensing area andwhether multiple die are employed. Further, while a die is taught, othersuitable sensors or sensor arrays may be mounted using techniquesdescribed herein. A preferred embodiment uses a single die sensor havingpixel sensor plates, an excitation signal reference plane, asemiconductor subtrate, and sense amps, or some othersemiconductor-based fingerprint reader that uses small RF signals todetect the fingerprint ridge and valley pattern. Such RF sensor signalsmay be employed in some cases to improve detection accuracy throughdirt, dead skin, or other contamination on the fingerprint surface.

FIG. 3 depicts an alternate embodiment of a circuit module 10 in whichdie 12 is enclosed at least partially around the bottom and 4 sides witha reinforcing layer 24. In this embodiment, reinforcing layer 24includes a high modulus material disposed in interior region 13 offlexible circuit 11 covering the bottom surface and sides of die 12. Thedie may be provided with a reinforcing layer 14 (FIG. 1), which is alsocovered. For example, overmolding, potting, encapsulation, or some othersuitable assembly method may be used for “ruggedizing” or protecting die12 from exposure to water, dust, oil, chemicals, extreme temperaturechanges, and jostling. One embodiment employs a high-durometer siliconerubber compound. Other suitable materials may be used for high-modulusmaterial 24 and low modulus material 26, and such materials may beselected based on their modulus and requirements such as expectedpressure, size and thickness of the die, for example. Preferredembodiments need encapsulation materials that will withstand reflowtemperatures for both tin lead solder and no lead solder so that module10 may be reflow-mounted to a circuit board, for example, in itsintended operating environment. Such a reinforcing layer 24 may extendabout the bottom-surface and sides of die 12 in a manner sufficient toat least partially protect the die from flexural loads. This embodimentis similar to the embodiment depicted in FIG. 1, except reinforcinglayer 24 here surrounds five sides of die 12, while reinforcing layer 14of FIG. 1 is only along the bottom side of die 12.

Die 12 (plus its enclosing reinforcing layer 24) may further be mountedwithin low modulus material 26 that surrounds the reinforced die 12. Thelow modulus material 26 may be disposed in interior region 13 and aboutthe high modulus material of reinforcing, layer 24 in a mannersufficient to at least partially absorb compressive loads applied to thedie. For example, having low modulus material 26 with a lower modulus ofelasticity than that of die 12 may help prevent damage to the diesurface from excessive force applied to a small area of the die'ssurface. This allows the reinforced die 12 to “float” oil the lowmodulus material 26 within flexible circuit 11.

Other features described herein may be added to the design depicted inFIG. 3, such as certain features described in reference to FIG. 1. Forexample, circuit module 10 of FIG. 3 may also utilize gap pattern 18(refer to FIG. 1) below die 12 (plus its reinforcing layer 24). Such agap pattern 18 may provide an initial pressure relief when a force isapplied to the exposed outer surface of die 12. In another example, theembodiment depicted in FIG. 3 may also utilize gaps 20 between the edgesof die 12 (plus its reinforcing layer 24) and the proximate edges of thelow modulus material 26. Such gaps 20 may reduce “peel force” in thepresence of a downward force on the top surface of die 12.

FIG. 4 depicts an alternate embodiment of circuit module 10 in which adry film adhesive 28 bonds at least part of the upper surface of die 12to flexible circuit 11. Such a dry film adhesive 28 may be compressibleand have a low modulus of elasticity, which can, for example, allow aforce applied to the surface of the flexible circuit 11 to betransmitted to die 12 beneath it.

Other features herein may be added to circuit module 10 depicted in FIG.4, such as certain features described in reference to FIGS. 1 and 3. Forexample, circuit module 10 of FIG. 4 may also utilize gap pattern 18(FIG. 1) below die 12 (plus its reinforcing layer 24). In anotherexample, the embodiment depicted in FIG. 4 may also utilize gaps 20between the edges of die 12 (plus its reinforcing layer 24) and theproximate edges of the low modulus material 26. In another example, theembodiment depicted in FIG. 4 may also utilize a dry film adhesive 28(FIG. 3) that bonds at least part of the upper surface of die 12 toflexible circuit 11.

FIG. 5 depicts exemplar peel force “gaps” 20 at the side edges of die 12according to one embodiment of the present invention. For example, voidscontaining no material can exist between the edges of die 12 and theproximate edges of the resilient low modulus material 16. Such gaps 20may reduce “peel force” in the presence of a downward force on the topsurface of die 12. Gaps 20 may reduce the concentration of stressesalong the edges of die 12 when forces on the top surface of die 12 wouldotherwise have the tendency to peel the polyimide window 23 Away fromthe die.

FIG. 6 is a flow chart of a process for making a circuit module 10according to another embodiment of the present invention. In thisembodiment, a dry film adhesive 28 bonds at least part of the uppersurface of die 12 to flexible circuit 11, such as that depicted in FIG.4. Step 601 provides a flexible circuit 11 and a die. Step 602 adds goldcontacts to flexible circuit 11 and the die. The die preferably has goldbumps whereas the flex circuit has gold pads, but bumps, built-up pads,or other suitable structures may also be formed on the flex circuit, orboth. Step 603 bonds die 12 to flexible circuit 11 with dry filmadhesive 28. Other adhesives such as liquid adhesives may be used.Preferable adhesives are thermal set, pressure sensitive adhesives. Theadhesive is preferably applied to the flex circuit and then the dieapplied thereto, but the opposite arrangement may be employed as well.In step 604, compression bonds are formed along oppositely disposedcontacts on flexible circuit 11. This may be done by known methods whichtypically involve heat and pressure applied over time to causeconductive metallic bonds to form. Step 605 provides a molded underfillform including the compressible low modulus material. Examples of themolded underfill are depicted in FIGS. 1, 3, 4 and 5 as low modulusmaterial 16 and 26. Step 606 folds flexible circuit 11 into a shapeabout the molded underfill, such as that having top side 15 and bottomside 17. Other embodiments may, of course, use other shapes for flexiblecircuit 11 than that depicted in FIG. 4. This can serve to protect die12 within flexible circuit 11.

FIG. 7. is a flow chart of a process for making a circuit moduleaccording to another embodiment of the present invention. In thisembodiment, die 12 is enclosed at least partially on five sides with areinforcing layer 24, such as that depicted in FIG. 3. Step 701 providesa flexible circuit 11. Step 702 adds gold contacts to the die,preferably as bumps. Step 703 bonds die 12 to flexible circuit 11 withan adhesive. In step 704, compression bonds are formed between goldcontacts on the die and oppositely disposed contacts on flexible circuit11. In step 705, reinforcing layer 24 is provided preferably as a moldedform of high modulus material. The form is preferably bonded to the die,which may be reinforced, and the flex circuit. Such high modulusmaterial may cover the bottom surface and sides of die 12, serving to atleast partially protect die 12 from flexural loads. In step 706, lowmodulus material 26 is provided preferably as a molded form and bondedbelow reinforcing layer 24. The low modulus for is provided such that,after flex circuit folding, it will fill part or all of interior region13 of flexible circuit 11. This allows the reinforced die 12 to “float”on the low modulus material 26 within flexible circuit 11. Step 707folds flexible circuit 11 into shape about the two forms, thus, in thisembodiment, building the depicted module in FIG. 3. The flex circuit itpreferably attached to the forms with adhesive.

FIG. 8 is a flow chart of a process for making a circuit module 10according to another embodiment of the present invention. In thisembodiment, a gap pattern 18 exists between the bottom of the reinforceddie 12 and the resilient low modulus material 16, such as that depictedin FIG. 1. Step 801 provides a flexible circuit 11. Step 802 adds goldcontacts to die such that they will oppositely match gold pads on theflexible circuit for compression bonding. Step 803 bonds die 12 toflexible circuit 11 with an adhesive. In step 804, compression bondsbetween gold contacts on die 12 and oppositely disposed gold contacts onflexible circuit 11. In step 805, gap pattern 18 is formed, or otherwiseadded, in a low modulus material molded form, preferably made as part ofthe molding process. In step 806, low modulus material 16 is provided,preferably as a molded form which is adhesively fixed to flexiblecircuit 11 in the area on flexible circuit 11 that, when folded, isbelow reinforcing layer 14. The low modulus material 16 is formed insufficient quantities such that interior region 13 is mostly filled withlow modulus material when flexible circuit 11 is folded. Step 807 foldsflexible circuit 11 into a shape and preferably fixes it to the formwith adhesive, such as that having top side 15 and bottom side 17.

While this specification describes several embodiments, these should notbe construed as limitations on the scope of the invention or of what maybe claimed. Certain features that are described in this specification inthe context of separate embodiments can also be implemented incombination in a single embodiment. Conversely, various features thatare described in the context of a single embodiment can also beimplemented in multiple embodiments separately or in any suitablesubcombination. Similarly, while operations are depicted in the drawingsin a particular order, this should not be understood as requiring thatsuch operations be performed in the particular order shown or insequential order, or that all illustrated operations be performed, toachieve desirable results.

1. A circuit module including: a flexible circuit having a first sideand a second side, and one or more conductive layers, a conductivefootprint expressed along the first side, the flexible circuit beingbent to form an interior region; a die electrically connected to theconductive footprint, the die having a top surface with a sensing area,a bottom surface, multiple sides, and a die coefficient of thermalexpansion; resilient low modulus material at least partially filling theinterior region of the flexible circuit, the low modulus materialdisposed about the bottom surface and sides of the die in a mannersufficient to at least partially absorb compressive loads from the die,a gap formed by at least one side of the die and a proximate edge of thelow modulus material.
 2. The circuit module of claim 1 furthercomprising a gap between all sides of the die and the low modulusmaterial, the gaps formed by respective sides of the die and proximateedges of the low modulus material.
 3. The circuit module of claim 1further comprising a reinforcing layer bonded to the back side of thedie, the reinforcing layer having a coefficient of thermal expansionwithin 5% of the die coefficient of thermal expansion, the reinforcinglayer having a high modulus of elasticity and a high tensile strength.4. The circuit module of claim 1 further comprising a reinforcing layerbonded to the back side of the die, the reinforcing layer having acoefficient of thermal expansion matching the die coefficient of thermalexpansion sufficiently to prevent thermal expansion stress faults, thereinforcing layer having a high tensile strength.
 5. The circuit moduleof claim 4 in which the reinforcing layer is comprised of a metal. 6.The circuit module of claim 1 further comprising a dry film adhesivebonding at least part of the upper surface of the die to the flexiblecircuit.
 7. The circuit module of claim 6 in which the dry film adhesiveis compressible and has a low modulus of elasticity.
 8. The circuitmodule of claim 1 further comprising a patterned gap formed in the lowmodulus material under the bottom surface of the die.
 9. The circuitmodule of claim 8 in which the patterned gap comprises voids shaped toprovide, between the voids, bumps that soften initial resistance of thelow modulus material to downward compressive forces on the die.
 10. Thecircuit module of claim 8 in which the patterned gap comprises multipleridges with voids formed therebetween.
 11. The circuit module of claim 1in which the sensing area comprises an RF fingerprint sensing array. 12.An electronic device comprising housing and a module according to claim1, in which the module is coupled to a circuit interior to the housing,and the sensing area is presented outside of the housing being coveredby a portion of the flexible circuit.
 13. A circuit module comprising: aflexible circuit having a first side and a second side, and one or moreconductive layers, and a conductive footprint expressed along the firstside, the flexible circuit being bent to form an interior region; a dieelectrically connected to the conductive footprint, the die having a topsurface with a sensing area, a bottom surface, multiple sides, and a diecoefficient of thermal expansion; a reinforcing layer bonded to the backside of the die, the reinforcing layer having a coefficient of thermalexpansion within 5% of the die coefficient of thermal expansion, thereinforcing layer having a high modulus of elasticity and a high tensilestrength.
 14. The circuit module of claim 13 further comprisingresilient low modulus material at least partially filling the interiorregion of the flexible circuit, the low modulus material disposed aboutthe bottom surface and sides of the die in a manner sufficient to atleast partially absorb compressive loads from the die.
 15. The circuitmodule of claim 14 further comprising a gap between the sides of the dieand the resilient low modulus material.
 16. The circuit module of claim13 further comprising: high modulus material disposed about the bottomsurface and sides of the die in a manner sufficient to at leastpartially protect the die from flexural loads; low modulus materialdisposed about the high modulus material in a manner sufficient to atleast partially absorb compressive loads applied to the die.
 17. Thecircuit module of claim 16 further comprising a gap between the sides ofthe die and the high modulus material.
 18. The circuit module of claim13 further comprising a dry film adhesive bonding at least part of theupper surface of the die to the flexible circuit.
 19. The circuit moduleof claim 13 in which the reinforcing layer has a modulus of elasticityof at least about 100 giga-Pascals.
 20. The circuit module of claim 13in which the flexible circuit comprises a metal-free zone disposed tocover the sensing area of the die.
 21. The circuit module of claim 13 inwhich the flexible circuit provides a polyimide window disposed to coverat least a portion of the sensing area of the die.
 22. The circuitmodule of claim 13 in which the reinforcing layer has a tensile strengthof at least about 100 mega-Pascals.
 23. The circuit module of claim 13in which the flexible circuit further comprises an array of modulecontacts for electrically connecting the circuit module to an operatingenvironment.
 24. An electronic device comprising housing and a circuitmodule according to claim 13, in which the circuit module is coupled toa circuit interior to the housing, and the sensing area is presentedoutside of the housing being covered by a portion of the flexiblecircuit.
 25. A circuit module including: a flexible circuit; a dieelectrically coupled to a conductive footprint, the die having a topsurface with a sensing area, a bottom surface and multiple sides; highmodulus material disposed the bottom surface and sides of the die in amanner sufficient to at least partially protect the die from flexuralloads; low modulus material disposed in an interior region and about thehigh modulus material in a manner sufficient to at least partiallyabsorb compressive loads applied to the die.
 26. The circuit module ofclaim 25 further comprising gaps between the sides of the die and thehigh modulus material, the gaps formed by respective sides of the dieand proximate edges of the high modulus material.
 27. The circuit moduleof claim 25 further comprising a reinforcing layer bonded to the backside of the die, the reinforcing layer having a coefficient of thermalexpansion within 5% of the die coefficient of thermal expansion, thereinforcing layer having a high modulus of elasticity and a high tensilestrength.
 28. The circuit module of claim 25 further comprising areinforcing layer bonded to the back side of the die, the reinforcinglayer having a coefficient of thermal expansion matching the diecoefficient of thermal expansion sufficiently to prevent thermalexpansion stress faults, the reinforcing layer having a high tensilestrength relative to that of the die.
 29. The circuit module of claim 25further comprising a dry film adhesive bonding at least part of theupper surface of the die to the flexible circuit.
 30. The circuit moduleof claim 25 in which the sensing area comprises an RF fingerprintsensing array.
 31. An electronic device comprising housing and a circuitmodule according to claim 25, in which the circuit module is coupled toa circuit interior to the housing, and the sensing area is presentedoutside of the housing being covered by a portion of the flexiblecircuit.
 32. A circuit module including: a flexible circuit having afirst side and a second side, and one or more conductive layers, aconductive footprint expressed along the first side, the flexiblecircuit being bent to form an interior region; a die electricallyconnected to the conductive footprint, the die having a top surface witha sensing area, a bottom surface, multiple sides, and a die coefficientof thermal expansion; resilient low modulus material at least partiallyfilling the interior region of the flexible circuit, the low modulusmaterial disposed about the bottom surface and sides of the die in amanner sufficient to at least partially absorb compressive loads fromthe die, the low modulus comprising a patterned gap formed in the lowmodulus material under the bottom surface or the die.
 33. The circuitmodule of claim 32 in which the patterned gap comprises voids shaped toprovide, between the voids, bumps that soften initial resistance of thelow modulus material to downward compressive forces on the die.
 34. Thecircuit module of claim 32 in which the patterned gap comprises multipleridges with voids formed therebetween.
 35. The circuit module of claim32 further comprising a gap between all sides of the die and the lowmodulus material, the gaps formed by respective sides of the die andproximate edges of the low modulus material.
 36. The circuit module ofclaim 32 further comprising a reinforcing layer bonded to the back sideof the die, the reinforcing layer having a coefficient of thermalexpansion within 5% of the die coefficient of thermal expansion, thereinforcing layer having a high modulus of elasticity and a high tensilestrength.
 37. The circuit module of claim 32 further comprising areinforcing layer bonded to the back side of the die, the reinforcinglayer having a coefficient of thermal expansion matching the diecoefficient of thermal expansion sufficiently to prevent thermalexpansion stress faults, the reinforcing layer having a high tensilestrength.
 38. The circuit module of claim 37 in which the reinforcinglayer is comprised of a metal.
 39. The circuit module of claim 32further comprising a dry film adhesive between at least part of theupper surface of the die to the flexible circuit.
 40. The circuit moduleof claim 39 in which the dry film adhesive is compressible and has a lowmodulus of elasticity.
 41. The circuit module of claim 32 in which thesensing area comprises an RF fingerprint sensing array.
 42. Anelectronic device comprising housing and a module according to claim 32,in which the module is coupled to a circuit interior to the housing, andthe sensing area is presented outside of the housing being covered by aportion of the flexible circuit.
 43. An electronic device comprisinghousing and a circuit module according to claim 32, in which the circuitmodule is coupled to a circuit interior to the housing, and the sensingarea is presented outside of the housing being covered by a portion ofthe flexible circuit.